Chp 11

Mutation rate: measured by counting the number of mutations affecting a phenotype and determining that frequency of mutations per base pair

Mutations are rare but genomes are genuinely considered to be stable!

Point mutations: occur at a specific position in a gene - in a gene (alter amino acid sequence) - in a regulatory region (affects gene expression levels)

Silent mutations are due to the reduction in the effectiveness of a codon to specify an amino acid, resulting in no change to the protein produced, thus maintaining the overall function of the gene.

Synonymous mutation: a type of silent mutation where a change in the nucleotide sequence does not alter the amino acid sequence of the protein, thereby preserving its function and stability.

Missense mutation: a type of point mutation where a single nucleotide change results in the substitution of one amino acid for another in the protein sequence, which can potentially alter the protein's function or stability.

Nonsense mutation: a type of point mutation that results in a premature stop codon in the amino acid sequence, leading to the truncation of the protein and often resulting in a loss of function.

Frameshift mutation: a type of mutation caused by insertions or deletions of nucleotides in the DNA sequence that shifts the reading frame of the codons, often resulting in a completely different and nonfunctional protein.

Triplet repeat expansion: a type of mutation characterized by the increase in the number of times a specific DNA sequence, typically consisting of three nucleotides, is repeated, which can lead to genetic disorders by disrupting normal gene function.

Depurination: the loss of a purine base (adenine or guanine) from the DNA molecule, which can result in mutations during DNA replication if not repaired properly.

Apurinic site: a site in DNA that has lost a purine base due to depurination, which can lead to replication errors and mutations if the missing base is not replaced.

Deamination: the removal of an amino group from a nucleotide, which can convert cytosine into uracil, causing base-pairing issues during DNA replication

Alkylating agents can result in base substitution mutations

Photoreactive repair: a DNA repair mechanism that uses visible light to repair damage caused by ultraviolet (UV) light - repairs thymine dimers

Nucleotide Excision Repair: a DNA repair mechanism that removes damage from DNA (also known as ultraviolet repair)

Nearly half of the human genome is composed of transposable DNA (47 or 48%)

Example: Given the sequence of triplet codons: 5’ - TAC AAA ATA CAG CGG - 3’, which of these sequences represents a nonsense mutation?

5’ - TAG AAA ATA CAG CGG - 3’ Changing TAC is changed to TAG (stop codon)

5’ - TAC AAA TAC AGC GGG - 3’

5’ - TAC AAG ATA CAG CGG - 3’

5’ - TAC AAA ATA CAC CGG - 3’